The present invention is directed toward the large area metallic filter elements which are used to filter high viscosity materials (approximately 200 to 20,000 poise) at relatively high temperatures (in excess of approximately 100.degree. C.) at relatively high pressures (in excess of approximately 400 p.s.i. guage differential). Prior art filters of this type traditionally include concentrically arranged dual filter media permanently affixed to appropriate support and mounting components to form the complete filter element to receive the filtrant through parallel flow paths for removing contaminants therefrom. The entire element is appropriately received within a housing or chamber through which the filtrant passes while being filtered.
In the prior art relating to such filter elements it has been customary to remove the filter element from the housing when it is no longer capable of accomplishing the desired cleansing of the filtrant and then cleaning the filter element for further use. It has been found that the life of the filter element is limited by the number of cleaning cycles the filter media is capable of withstanding. When the prior art filter media becomes no longer useful, that is, it can no longer be cleaned sufficiently to allow it to efficiently remove contaminants from the filtrant, the entire filter element is discarded. Although the filter media is no longer capable of continued efficient use the remaining components of the filter element could have additional life but for the inoperable filter media.
Prior art U.S. Pat. No. 4,218,324 issued Aug. 19, 1980 to W. U. Hartmann et al discloses a stainless steel metallic filter element of relatively small diameter constructed in such a manner that the filter media member may be removed and cleaned and replaced for further use by slipping the filter media over the outer surface of an appropriate support member. While the structure disclosed in U.S. Pat. No. 4,218,324 operates excellently for the small size filter elements, it has been found that it is inappropriate to the large area dual filter media filter elements of the present invention.
The U.S. Pat. No. 2,448,157 to Schneider discloses a dual filter media portable filter in which the filter media is a spun glass woven knitted or otherwise fabricated mesh stretched over a pair of cylindrical perforate shells for filtering liquid contained within an open tank such as an electroplating bath. The spun glass fabric may be removed from the shells for washing or replacement. The filter element as disclosed in the Schneider U.S. Pat. No. 2,448,157 is not usable with the filtrant employed with the filter elements constructed in accordance with the present invention.
Additional prior art patents known to applicants are: U.S. Pat. Nos. 1,918,980, 3,312,349, 3,653,512, 3,750,889, 3,883,430, 3,900,401, 4,167,483 and 4,179,372.